Envelope housing is broadly characterized by having spaced inner and outer insulating walls which form an air circulating space around the roof and wall sections of a building as well as the lower space contiguous to the earth. For instance, the envelope house may include a passive solar heating system on the southern exposed portion, a double wall on the north and heavily insulated single walls on the east and west portions. The sourthern exposed portion and the northern wall are connected to a lower air space and double ceiling in a manner which permits air to flow freely along all of the surfaces on the south, north, top and bottom of the structure. Envelope houses of the type described have also been employed in combination with earth-coupled lower air spaces; or in other words, the lower space is extended beneath the frost line so as to maintain the optimum mean temperature conditions in the lower space. For instance, in colder climates where the outside air temperature may vary as much as 100.degree. F. to 120.degree. F. from summer to winter, the temperature of the earth below the frost line will undergo little or no variation. Thus, notwithstanding a swing in temperature between 0.degree. F. and 100.degree. F., the variation in the earth temperature four feet below the earth's surface will be on the order of 45.degree. F. to 55.degree. F. Utilization of this earth-coupled effect as a part of the air circulating space for the envelope housing enables the earth to moderate the envelope's natural heat loss to the outside at night, or during cool spells. Since the envelope constitutes a mini-environment around the main living space or area of a house, its temperature can be maintained at or above the mean temperature of the lower space so long as there is uniform distribution of air throughout the envelope. As a result, any external heating source utilized, whether it be solar heating or otherwise, need only compensate for the temperature differential between the mean temperature of the earth below the frost line and the desired temperature level in the room air spaces of the housing.
It is known to utilize solar energy as a heat source in combination with envelope housing in order to elevate the temperature of the air circulating through the envelope and to transfer it to the earth for storage and for subsequent use as a heat supply supplementary to the heat of the earth and in this way minimize requirements for other auxiliary heat sources. Representative of such housing is the housing structure disclosed in U.S. Pat. No. 2,559,869 to Gay. This intent ignores the great difference between the specific heat of air and that of earth. Because of that difference, it is very difficult to heat earth with air, but very easy to heat air with earth. Major drawbacks in the utilization of solar heating systems, particularly those of the passive variety, are that they are somewhat localized in the sense that their rays are concentrated on the southern exposed sides of a house. Even where sophisticated heat storage systems are employed, it is difficult to achieve uniform temperature levels throughout the house, especially along the northern wall which typically is not exposed directly to sunlight. Envelope housing employed in combination with solar heating affords one means of improved air circulation, at least around the perimeter of the house, but nevertheless has not in the past achieved uniform air circulation throughout the entire structure. For example, U.S. Pat. No. 4,207,865 to Allen in which a passive solar system takes the form of a clerestory for directing heat onto a central partition and has incorporated in the partition a fluid circuit line. Among other things, the fluid circuit line is capable of distribution of heat from a central or intermediate heat source but falls short of uniform air circulation which is required throughout the year. Other representative patents are U.S. Pat. Nos. 3,142,728 to Thomason; 3,894,369 to Schmitt et al; 4,054,246 to Johnson; 4,119,084 to Eckels; 4,143,815 to Meysenburg; and 4,147,300 to Milburn, Jr.